This invention relates to the production of alkenediols. In a specific aspect, the invention relates to the production of alkenediols, and particularly 2-butene-1,4-diol, according to a series of reactions in which only conjugated diene, water and oxygen are consumed.
2-butene-1,4-diol is well known as a solvent in various chemical processes and as a starting material for the production of 2,5-dihydrofuran, another useful solvent. Further, 2-butene-1,4-diol can be hydrogenated to 1,4-butanediol which is used in the production of tetrahydrofuran, certain polyesters and polyurethanes.
In the past, a number of methods have been proposed for the production of 2-butene-1,4-diol and other alkenediols. One such method, disclosed in Sakomura et al., U.S. Pat. No. 3,911,032 (Oct. 7, 1975), involves hydrolysis of 1,4-dichloro-2-butene in an aqueous solution of alkali metal formate. According to this proposal, conversion of 1,4-dichloro-2-butene to 2-butene-1,4-diol is substantially complete. Further, substantially complete conversion of mixed dichlorobutene isomers to 2-butene-1,4-diol can be accomplished by conducting the hydrolysis reaction in the presence of elemental copper, iron, or zinc or a halide, formate, oxide, carbonyl or hydroxide thereof.
Vasey et al., U.S. Pat. No. 4,160,115 (July 3, 1979) discloses preparation of 2-butene-1,4-diol by reaction of butadiene with water and oxygen in the presence of copper, nickel, cobalt, chromium, manganese, molybdenum or a halide or organic acid salt thereof. The reaction is conducted at 50.degree. to about 150.degree. C., preferably in a water-miscible solvent.
Childs, U.S. Pat. No. 4,164,616 (Aug. 14, 1979) discloses preparation of alkanediols and alkenediols by a series of reactions involving halogenation of conjugated diene with molecular chlorine, bromine or iodine; acetolysis of the result in the presence of a salt of an alkali metal or alkaline earth metal, dissolved or dispersed in an organic acid solvent, to form diacetoxyalkene; hydrogenation of diacetoxyalkene to the corresponding diacetoxyalkane; hydrolysis of diacetoxyalkane to 1,4-alkanediol, preferably under basic conditions using an alkali or alkaline earth hydroxide; and regeneration of starting materials by passing an electric current through an aqueous solution of by-product metal halide from the acetolysis step to regenerate halogen for use in the halogenation step, hydrogen for use in the hydrogenation step and metal hydroxide for use in the hydrolysis step. The sequence of the hydrogenation and hydrolysis steps may be reversed according to the patentee.
Although alkenediols can be obtained according to the above-described processes, various disadvantages are encountered. For example, the dichlorobutenes employed as starting materials in the process of Sakomura et al. are expensive and the hydrolysis reaction results in formation of alkali metal chlorides which must be disposed of. Further, recovery of metal formate from the hydrolysis mixture requires neutralization with caustic. Accordingly, in the overall reaction scheme of the Sakomura et al. process, valuable chlorine and caustic are consumed and less valuable metal chlorides are formed. The process of Vasey et al. suffers from low yields and conversion rates as shown in the examples. Further, provision is not made for regeneration of starting materials. Such problems are avoided in the process of Childs; however, that process is relatively complex and the use of electricity for regeneration adds cost to the process.
Accordingly, it would be desirable to provide an improved process for preparation of alkenediols. It is an object of this invention to provide such a process. A further object of the invention is to provide an improved process for the preparation of high yields of alkenediols without consumption of costly reactants. A further object of the invention is to provide for the preparation of alkenediols according to a series of reactions wherein only conjugated diene, water and oxygen are consumed. A specific object of the invention is to provide an improved process for the preparation of 2-butene-1,4-diol wherein only 1,3-butadiene, water and oxygen are consumed. Other objects of the invention will be apparent to persons of skill in the art from the following description and the appended claims.
It has now been found that the objects of this invention can be attained by contacting dibromoalkenes with alkali metal formate under conditions effective to hydrolyze the dibromoalkenes to alkenediols. According to a preferred embodiment of the invention, dibromoalkenes prepared by bromination of conjugated diene with cupric bromide are hydrolyzed in the presence of aqueous alkali metal formate, and cuprous bromide, alkali metal bromide and formic acid generated in the bromination and hydrolysis steps are contacted with molecular oxygen under conditions effective to regenerate cupric bromide and sodium formate which can be re-used in bromination and hydrolysis.
Advantageously, preparation of alkenediols according to this invention results in high yields of the desired products. Further, according to a preferred embodiment of the invention, high yields of alkenediols are obtained according to an overall reaction scheme in which only conjugated diene, water and oxygen are consumed. The present invention gives particularly good results when employed in the production of 2-butene-1,4-diol from dibromobutenes as hydrolysis of the latter in the presence of alkali metal formate results in substantially complete hydrolysis of 1,4-dibromo-2-butene isomer to 2-butene-1,4-diol, and in addition, isomerization takes place such that at least a portion of any 3,4-dibromo-1-butene present in the intial charge is converted to 2-butene-1,4-diol. Accordingly, costly separation operations and the use of additional metals or compounds thereof are not required. According to a particularly advantageous embodiment of the invention, 2-butene-1,4-diol is prepared by a continuous process involving bromination of 1,3-butadiene in the presence of cupric bromide, followed by hydrolysis of the resulting dibromobutenes in the presence of alkali metal formate to form high yields of 2-butene-1,4-diol, with regeneration of cupric bromide and metal formate and recycle thereof. The process according to this aspect of the invention can be represented as follows: EQU H.sub.2 C:CHCH:CH.sub.2 +2CuBr.sub.2 .fwdarw.BrH.sub.2 CCH:CHCH.sub.2 Br+2CuBr EQU BrH.sub.2 CCH:CHCH.sub.2 Br+2H.sub.2 O+2MOOCH.fwdarw.HOH.sub.2 CCH:CHCH.sub.2 OH+2MBr+2HOOCH EQU 2CuBr+2MBr+2HOOCH+1/2O.sub.2 .fwdarw.2CuBr.sub.2 +2MOOCH+H.sub.2 O
As used above, M represents alkali metal. The net reaction from the above is as follows: EQU H.sub.2 C:CHCH:CH.sub.2 +H.sub.2 O+1/2O.sub.2 .fwdarw.HOH.sub.2 CCH:CHCH.sub.2 OH